A wide variety of interferometric imaging techniques have been developed to provide high resolution structural information in a wide range of applications. Optical Coherence Tomography (OCT) is a technique for performing high-resolution cross-sectional imaging that can provide images of samples including tissue structure on the micron scale in situ and in real time (Huang et al., 1991). OCT is an interferometric imaging method that determines the scattering profile of a sample along the OCT beam by detecting light reflected from a sample combined with a reference beam. Each scattering profile in the depth direction (z) is called an axial scan, or A-scan. Cross-sectional images (B-scans), and by extension 3D volumes, are built up from many A-scans, with the OCT beam moved to a set of transverse (x and y) locations on the sample.
Many variants of OCT have been developed where different combinations of light sources, scanning configurations, and detection schemes are employed. In time domain OCT (TD-OCT), the path length between light returning from the sample and reference light is translated longitudinally in time to recover the depth information in the sample. In frequency domain or Fourier domain OCT (FD-OCT), the broadband interference between reflected sample light and reference light is acquired in the spectral domain and a Fourier transform is used to recover the depth information. The sensitivity advantage of frequency-domain optical coherence tomography (OCT) over time-domain OCT is well established (Choma, Sarunic, Yang, & Izatt, 2003; Leitgeb, Hitzenberger, & Fercher, 2003).
There are two common approaches to FD-OCT. One is spectral domain OCT (SD-OCT) where the interfering light is spectrally dispersed prior to detection and the full depth information can be recovered from a single exposure. The second is swept-source OCT (SS-OCT) where the source is swept over a range of frequencies and detected over time, therefore encoding the spectral information in the time dimension. In traditional point scanning or flying spot techniques, a single point of light is scanned across the sample. In parallel techniques, a series of spots, a line of light (line-field), or a two-dimensional array of light (full-field or partial field) are directed to the sample. The resulting reflected light is combined with reference light and detected. Parallel techniques can be accomplished in TD-OCT, SD-OCT or SS-OCT configurations. (Lee & Kim, 2008; Mujat, Iftimia, Ferguson, & Hammer, 2009; Nakamura et al., 2007)
The related fields of optical diffraction tomography, holoscopy, digital interference holography, holographic OCT, and interferometric synthetic aperture microscopy (Hillman, Luhrs, Bonin, Koch, & Huttmann, 2011; Kim, 2000; Ralston, Marks, Scott Carney, & Boppart, 2007) are also interferometric imaging techniques that can be accomplished in parallel and in particular line-field scanning configurations (see for example U.S. patent application Ser. No. 13/745,632 hereby incorporated by reference).
Interferometric imaging with swept sources may suffer from motion artifacts caused by axial motion of scatterers. An axial moving scatterer can cause three different artifacts, axial point spread function (PSF) broadening, transverse PSF broadening as well as an axial shift. The axial shift, caused by a Doppler shift proportional to the axial velocity of the moving scatterer, may be the most critical of the three. Especially when imaging the human eye at relatively low sweep rates, the signal from the blood inside the retinal blood vessels may appear to be shifted up or down within the image. This may cause significant confusion among operators and could potentially lead to misdiagnosis. It is therefore desirable to develop systems and methods for attenuating the signal of moving scatterers in swept-source interferometric imaging techniques.